Rotary gas compressor



r Patented Apr. 21, 1964 RIARY GAS CORESSOR John Cmllo, Kings Park, N.Y., assignor to Fairchild Stratos Corporation, Hagerstown, Md., a corporation of Maryland Fiied Feb. 29, 1952, Ser. No. 174,429 4 Claims. (Cl. 230 141 The present inventon relates to rotary gas compressors and particularly to a Gerotor type pump utilized for compressing gas. The Gerotor pump is basically an internal gear type positive displacement pump having two rotors or gears, one of which is within and eccentric to the other, the rotors having tooth divisions, with contours on each outlined by the tooth form of the other at regular angular motion and the outer rotor having one tooth division more than the inner rotor. In the past, such pumps have been used for the pumping of liquids only, since in the form in Which heretofore constructed, they could not serve to compress gases efficiently.

In my present invention the Gerotor is aclapted to the compressing of gases by modifying the size and shape of the discharge port. Thus as the lobe space between the two rotors of the pump diminishes the gas is retained theren and compressed, being discharged when and only when the desired pressure, in terms of the compression ratio, has been attained. This is accomplished by so locating, dimensioning and shaping the port as to cause the discharge to be immediate once the desired compression ratio has been reached. This modification of the Gerotor type pump not only produces an efiicient gas compressor, but also retains the advantage of extremely small size thus producing a compressor which is particularly adapted for airborne usage.

Furthermore, as has been indicated, the gas compressor may be assembled from readily available parts, that is, the normal internally toothed and externally toothed internal gear arrangement of the usual Gerotor pump,

the only modification necessary being in the formation of the discharge port or ports.

It is an object of the invention to provide a gas compressor which is generally similar to the Gerotor type of internal gear positive displacement pump.

- It is another object of the invention to provide such a gas compressor in which a desired compressor ratio .may be obtained by simply designing the discharge port or ports to produce that desired compression ratio assuring that there Will be no leakage into the discharge ports prior to the time that the desired pressure has been attained and that once that pressure has been attained the discharge from the tooth spaces will be substantially in- .stantaneous.

Other objects and features of the invention will be apparent When the following description is considered in male and female rotors of the pump showing the relative position of the two parts just prior to the time of discharge of the compressed gas into the discharge port .or ports;

FIGURE 3 is a transverse cross-sectional view of the .assembled device of FGURE 1 showing the position of the male and female rotors at the moment when the space between a pair of the male and female rotors has just been filled with gas and compression is started. This view.also shows gas being discharged from the reduced space between other lobes of the male and female rotor into the discharge passageway;

ing member 10 and serve to seal the rotors 12 FIGURE 4 is a view similar to FIGURE 3 but showing the rotors further advanced to the point where dis charge of the compressed gas has been substantially completed; and

FIGURE 5 is a diagram showing the mode of designing the discharge ports as functions of the rotor geometry and the desired compression ratio.

Referring now to the drawings and particularly to FIGURE 1, there is shown therein a housing member 10 which has a bore 11 therein which bore is eccentric to the outer periphery of the member 10. Mounted in the bore 11 is a female rotor 12, having in the particular instance shown, seven teeth 13 and a corresponding number of lobes 14. A

Mounted within the female rotor 12 is a male rotor 15 which rotor is keyed to a shaft 16, the shaft being mounted concentrically with respect to the housing end members 17 and 18. These housing end members are normally of the same diameter and configuration as the housand 15 from atmosphere. r r

The male rotor 15 in the usual manner has one less tooth than the female rotor 12 thus in the particular instance having six teeth. Each end plate or housing member 17 and 18 is provided with an inlet port 20 of the usual kidney shape common in Gerotor pumps and is additionally supplied with a discharge port 21 which ds charge port is of such a size and so shaped that it provides substantially instantaneous discharge of the compressed gas once the desired compression ratio has been attained, while assuring that there Will be no leakage of gas from the compression Chamber to the discharge port until that compression ratio has been attained.

As is usual, thhousing member 10 and end plates 17 and 18 are provided with aligned apertures 22 through which bolts are passed, the nuts placed thereon then serving to draw the ports tightly together and to bring the sealing gasket 23, inserted in a groove in each end plate 17 or 18, into engagement with the respective flat facing surface of housing member 10 thereby sealing the unit.

7 As has been indicated, the design of the discharge port or ports (it being only necessary that a single port in one of the end plates be utilized, but preferable that each end plate have such ports) is the essence of my invention and makes it possible to utilize a unit which heretofore has been widely and favorably known as a liquid pump only, as a gas compressor. The method of laying out this port is shown particularly in FIGURE 5 which figure shows the various rotor radii and relatos these dimensons to a particular position of the rotors in Which a lobe space has just been filled, this same relationship being shown in FIGURE 3.

Referring now to FIGURE 3, the space 24 between rotors 12 and 15 is the space which has just been filled with gas which has been supplied through the inlet port 2'0. The center line designated 25 is the line which passes through the center of lobe or tooth space 24, through the center 26 of the female rotor and through the center 27 of the male rotor. This center line and these centers have been given the same reference characters in FIG- URE 5. With this position of the rotors as a starting point, the angle 0 is laid off about the center 27 thus making it possible to draw a radial line 28 from that center outwardly and intersecting the aro 30 which is an aro of the root circumference of the female rotor, the radius of which root circle has been designated F The angie 0 is the angle at which the desired compression ratio is attained which can be determined experimentally or by calculating the decrease in the space between the rotor lobes as the male rotor is driven and the female rotor drive1i by it.

The distance between the centers 26 and 27 is the eccentricity of the female rotor relative to the true center represented by the center of the male rotor and of the shaft 16. This distance has been designated on the drawing as e. The ratio of the number of lobes of the male rotor (N to the number of lobes of the female rotor (N is multiplied by thus giving an angle always smaller than 0. This second angle is laid out about the center 26 and a radial line 31 drawn. Thereafter a line 32 is drawn parallel to, above and spaced from the line 31 by the distance e. The boundary of the discharge port extends inwardly along the line 32 until that line intersects an arc struck about the center 27 with the outer radius of the male lobe (R as its radius.

Next an arc of radius R equal to the lobe radius of the the male rotor, is struck from the point at which arc 30 intersects line 28. An intersection of this arc with the arc of radius R determines the point 33 in the port outline. The arc of radius R terminates where that arc intersects the radial line 28 thus determinng the point 34 of the lobe outline. From point 34 the lobe Outline extends to the point 35 which point is a point on the circumference F 180 removed in the direction of rotation from the filled lobe space.

As shown in the drawings, the line 36 connecting points 34 and 35 does so by means of fillet curves 37. This, however, is not essential although it is desirable for ease in manufacture. Also, although the line 36 is shown as straight, this is not necessary it being essential only that the connection between points 34 and 35 extend through the point such as that indicated at 38 (FIG. 3) at which the male and female rotor lobes are in substantially complete engagement.

From the point 35 the port outline extends in a direction counter to the indicated direction of rotation to the point 40 which point is that at which the description of the discharge port outline started. Again for case of manufacturing fillet curves are supplied at the corners so that at the lower end of the discharge port, as seen in FIGURES 2 through 5, is not square, but is rounded oif.

Referring now particularly to FIGURE 2, it will be seen that during the rotation from the position shown in FIGURE 3, to that shown in FIGURE 2, the space 24 between lobes of the male and female rotors has been diminished and in the particular showing of FIGURE 3 the volumetric capacity of the lobe space has been decreased to produce the desired compression ratio. It will be noticed that the upper tail-like portion 41 conforms to the arc R of the discharge port, but that no discharge has yet been permitted to occur.

Referring now to FIGURE 3, it will be noted that in that figure the space 24 between the respective lobes is in communication with the discharge port not only at its end, but also at the opposite end where the tail portion 41 occurs.

Referring now to FIGURE 4, it will be seen that at this point the lobe bearing the compressed gas is still in communication with the discharge port throughout a major portion of its remaining area. Thus the gas compressed in the lobe space is virtually instantaneously dis charged once the rotors have reached the desired position corresponding to the desired compression ratio, but due to the shape of the port no discharge occurs in ad- Vance of attaining that compression ratio.

It is desirable that the gas to be compressed have a small amount of lubrication such as oil in suspension therein in order to aid in sealing the device.

It Will be obvious from the foregoing discussion that the exact shape and size of the port depends solely upon the geometry of the mating rotors and the desred com- 4 pression ratio and that therefore although the axact shape and size of the port will vary, there Will be a single shape and size used with a particular pair of rotors to achieve a particular desired compression ratio.

lt will also be obvious that the male rotor may be operated on an eccentric portion of a shaft supported in the same manner as is the shaft 16 and the female rotor mounted in a bore concentric to the shaft 16 and thus eccentric as respects the center of the male rotor.

As indicated hereinabove, the extreme radally outward and radially inward boundaries of the discharge port need not be exactly where defined above, since radially outward movement of the circle arc of the female rotor radius would cause that boundary to coincide With a solid portion of the rotor and would not alter the effective discharge port arca and, in a like manner, movement of the boundary defined by line 36, while keeping all portions of the line or curve within the boundaries of the male rotor, would not affect the effective discharge port area.

While I have described a preferred embodiment of the invention, it will be understood that I wish to be limited not by the foregoing description, but solely by the claims granted to me.

l. In a Gerotor compressor of the type having a lobed female rotor, a lobed male rotor having one less lobe than said female rotor, a housing member having a bore in which said female rotor is rotatably mounted, closure members at the sides of said housing member, said closure members carrying a shaft on which said male rotor is mounted, said bore and said male rotor shaft mounting being eccentric with respect to each other, the center of one of said rotors being concentric to said shaft and the center of the other rotor being eccentric to said shaft, all lobes of one of said rotors being in sealing contact with the lobes of the other of said rotors at least one of said closure members having an inlet port of usual kidney shape; the improvement which comprises providing a discharge port in at least one of said closure members which is substantially the pr0jection of a figure bounded by a line extending from a point lying on a circle arc having the root radius of said female rotor, laicl off about a center coinciding with the center of the concentrically mounted rotor, said point being removed in the direction of rotation from a diameter extending through the center of the male and female rotor lobe space which is filled at the start of compression, and through the centers of said male and female rotors at that position, by an arc comprising the arc subtended by an angle measured about the center of said eccentrically mounted rotor which angle is equal to the ratio of the number of lobes in the male rotor to the number of lobes in the female rotor multiplied by the angle measured about the center of the concentrically mounted rotor at which the desired compression ratio occurs, and the arc of said root radius circle subtended by a chord equal to the eccentric distance; thence inwardly along a line parallel to the radial line defining said first mentioned angle to a point on a second circle arc having a radius equal to the outer radius of the male rotor, said arc being struck about the center of the concentrically mounted rotor; thence in the direction of rotation along said second circle arc to a point at which that arc is intersected by an arc of the male rotor lobe radius struck from the point on said first circle arc angularly spaced from said center line by said desired compression ratio angle; thence along said male rotor lobe radius arc in a direction generally counter to the direction of rotation to the intersection of said arc with the radial line extending to the center of said concentrically mounted rotor from the point from which said arc was struck; thence through a point at which the female lobe and male lobe space are in substantially complete engagement to a point on said first circle arc removed substantially in the direction of rotation from the center line of said filled rotor lobes; and thence along said first circle arc to the place of beginning.

2. In a Gerotor compressor of the type having a lobed female rotor, a lobed male rotor having one less lobe than said female rotor, a housing member having a bore in which said female rotor is rotatably mounted, closure members at the sides of said housing members, said closure members carrying a rotatable shaft on which said male member is fixed, said bore being eccentric with respect to said male rotor shaft, the center of one of said rotors being concentrc to said shaft and the center of the other rotor being eccentric to said shaft, all lobes of one of said rotors being in sealing contact with the lobes of the other of said rotors at least one of said closure members having an inlet port of usual kidney shape; the improvement which comprises providing a discharge port in at least one of said closure members which is substantially the projection of a figure bounded by a line extending from a point lying on a circle arc having the root radius of said female rotor, laid ofi' about the center of the male rotor, said point being removed in the direction of rotation from a diameter extending through the center of the male and female rotor lobe space which is filled at the start of compression, and through the centers of said male and female rotors at that position, by an arc comprising the arc subtended by a first angle measured about the center of said female rotor which first angle is equal to the ratio of the number of lobes in the male rotor to the number of lobes in the female rotor multiplied by a second angle measured about the center of the male rotor at which the desired compression ratio occurs, and the arc of said root radius circle subtended by a chord equal to the eccentric distance; thence inwardly along a line parallel to the radial line defining said first mentioned angle to a point on a second circle arc having a radius equal to the outer radius of the male rotor, said arc being struck about the center of the male rotor; thence in the direction of rotation along said second circle arc to a point at which that arc is intersected by an arc of the male rotor lobe radius struck from the point on said first circle arc angularly spaced from said center line by said desired compression ratio angle; thence along said male rotor lobe radius arc in a direction generally counter to the direction of rotation to the intersection of said arc with the radial line extending to the center of said male rotor from the point from which said arc was struck; thence through a point at which the female lobe and male lobe space are in substantially complete engagement to a point on said first circle arc removed substantially 180 in the direction of rotation from the center line of said filled rotor lobes; and thence along said first circle arc to the place of beginning.

3. In a Gerotor compressor of the type having a lobed female rotor, a lobed male rotor having one less lobe than said female rotor, a housing member having a bore in which said female rotor is rotatably mounted, closure members at the sides of said housing members, said closure members carrying a shaft on which said male member is mounted, said bore and said male rotor shaft mounting being eccentric with respect to each other, all lobes of said male rotor being in sealing contact with lobes of said female rotor at least one of said closure members having an inlet port of usual kidney shape; the improvement which comprises providing a discharge port in at least one of said closure members which is substantially the projection of a figure bounded by a line extending from a point lying on a circle arc having the root radius of said female rotor, laid off about a center coinciding with the center of the concentrically mounted rotor, said point being removed in the direction of rotation from a diameter extending through the center of the male and female rotor lobe space which is filled at the start of compression, and through the centers of said male and female rotors at that position, by an arc comprising the arc subtended by an angle measured about the center of said eccentrically mounted rotor wherein 0 is the angle measured about the center of the concentrically mounted rotor from said diameter to the point at which the desired compression ratio occurs, N is the number of lobes of the male rotor and N is the number of lobes of the female rotor, and the arc of said root radius circle subtended by a chord equal to the eccentric distance; thence inwardly along a line parallel to the radial line defining said angle to a point on a second circle arc having a radius equal to the outer radius of the male rotor, said arc being struck about the center of the concentrically mounted rotor; thence in the direction of rotation along said seoond circle arc to a point at which that arc is intersected by an arc of the male rotor lobe radius struck from the point on said first circle arc angularly spaced from said center line by said angle thence along said male rotor lobe radius arc in a direction generally counter to the direction of rotation to the intersection of said arc with the radial line extending to the center of said concentrically mounted rotor from the point from which said arc was struck; thence through a point at which the female lobe and male lobe space are in substantially complete engagement to a point on said first circle arc removed substantially in the direction of rotation from the center line of said filled rotor lobes; and thence along said first circle arc to the place of beginning.

4. In a Gerotor compressor of the type having a lobed female rotor, a lobed male rotor having one less lobe than said female rotor, a housing member having a bore in which said female rotor is rotatably mounted, closure members at the sides of said housing members, said closure members carrying a rotatable shaft on which said male member is fixed, said bore being eccentric With respect to said male rotor shaft, all lobes of said male rotor being in sealing contact with lobes of said female rotor at least one of said closure members having an inlet port of usual kidney shape; the improvement which comprises providing a discharge port in at least one of said closure members which is substantially the projection of a figure bounded by a line extending from a point lying on circle arc having the root radius of said female rotor, laid off about the center of the male rotor, said point being removed in the direction of rotation from a diameter extending through the center of the male and female rotor lobe space which is filled at the start of compression, and through the centers of said male and female rotors at that position, by an arc comprising the arc subtended by an angle m NF9 measured about the center of said female rotor wherein 9 is the angle measured about the center of the male rotor from said diameter to the point at which the desired compression ratio occurs, N is the number of lobes of the male rotor and N is the number of lobes of the female rotor, and the arc of said root radius circle subtended by a chord equal to the eccentric distance; thence inwardly along a line parallel to the radial line defining said angle to a point on a second circle arc having a radius equal to the outer radius of the male rotor, said arc being struck about the center of the male rotor; thence in the direction of rotation along said second circle arc to a point at 7. which that aro is ntersected by an are of the male rotor lobe radius struck from the point on said first circle are angularly spaced from said center line by said angle 6; thence along said male rotor lobe radius are in a direction generally counter to the direction of rotation to the intersection of said are With the radial line extending to the center of said male rotor from the point from Which said arc Was struck; thence through a point at which the female lobe and male lobe space are in substantially complete engagement to a point 011 said first circle are removed substantially 180 in the direction of rotation from the center line of said filled rotor lobes; and thence along said first circle arc to the place of beginning.

References Cted in the file of this patent UNITED STATES PATENTS 1,486,835 Hill Mar. 11, 1924 1,682,564 Hill Aug. 28, 1928 1,682,565 Hill Aug. 28, 1928 2,386,896 Hill et al. Oct. 16, 1945 2,693,313 McAdam Nov. 2, 1954 

1. IN A "GEROTOR" COMPRESSOR OF THE TYPE HAVING A LOBED FEMALE ROTOR, A LOBED MALE ROTOR HAVING ONE LESS LOBE THAN SAID FEMALE ROTOR, A HOUSING MEMBER HAVING A BORE IN WHICH SAID FEMALE ROTOR IS ROTATABLY MOUNTED, CLOSURE MEMBERS AT THE SIDES OF SAID HOUSING MEMBER, SAID CLOSURE MEMBERS CARRYING A SHAFT ON WHICH SAID MALE ROTOR IS MOUNTED, SAID BORE AND SAID MALE ROTOR SHAFT MOUNTING BEING ECCENTRIC WITH RESPECT TO EACH OTHER, THE CENTER OF ONE OF SAID ROTORS BEING CONCENTRIC TO SAID SHAFT AND THE CENTER OF THE OTHER ROTOR BEING ECCENTRIC TO SAID SHAFT, ALL LOBES OF ONE OF SAID ROTORS BEING IN SEALING CONTACT WITH THE LOBES OF THE OTHER OF SAID ROTORS AT LEAST ONE OF SAID CLOSURE MEMBERS HAVING AN INLET PORT OF USUAL KIDNEY SHAPE; THE IMPROVEMENT WHICH COMPRISES PROVIDING A DISCHARGE PORT IN AT LEAST ONE OF SAID CLOSURE MEMBERS WHICH IS SUBSTANTIALLY THE PROJECTION OF A FIGURE BOUNDED BY A LINE EXTENDING FROM A POINT LYING ON A CIRCLE ARC HAVING THE ROOT RADIUS OF SAID FEMALE ROTOR, LAID OFF ABOUT A CENTER COINCIDING WITH THE CENTER OF THE CONCENTRICALLY MOUNTED ROTOR, SAID POINT BEING REMOVED IN THE DIRECTION OF ROTATION FROM A DIAMETER EXTENDING THROUGH THE CENTER OF THE MALE AND FEMALE ROTOR LOBE SPACE WHICH IS FILLED AT THE START OF COMPRESSION, AND THROUGH THE CENTERS OF SAID MALE AND FEMALE ROTORS AT THAT POSITION, BY AN ARC COMPRISING THE ARC SUBTENDED BY AN ANGLE MEASURED ABOUT THE CENTER OF SAID ECCENTRICALLY MOUNTED ROTOR WHICH ANGLE IS EQUAL TO THE RATIO OF THE NUMBER OF LOBES IN THE MALE ROTOR TO THE NUMBER OF LOBES IN THE FEMALE ROTOR MULTIPLIED BY THE ANGLE MEASURED ABOUT THE CENTER OF THE CONCENTRICALLY MOUNTED ROTOR AT WHICH THE DESIRED COMPRESSION RATIO OCCURS, AND THE ARC OF SAID ROOT RADIUS CIRCLE SUBTENDED BY A CHORD EQUAL TO THE ECCENTRIC DISTANCE; THENCE INWARDLY ALONG A LINE PARALLEL TO THE RADIAL LINE DEFINING SAID FIRST MENTIONED ANGLE TO A POINT ON A SECOND CIRCLE ARC HAVING A RADIUS EQUAL TO THE OUTER RADIUS OF THE MALE ROTOR, SAID ARC BEING STRUCK ABOUT THE CENTER OF THE CONCENTRICALLY MOUNTED ROTOR; THENCE IN THE DIRECTION OF ROTATION ALONG SAID SECOND CIRCLE ARC TO A POINT AT WHICH THAT ARC IS INTERSECTED BY AN ARC OF THE MALE ROTOR LOBE RADIUS STRUCK FROM THE POINT ON SAID FIRST CIRCLE ARC ANGULARLY SPACED FROM SAID CENTER LINE BY SAID DESIRED COMPRESSION RATIO ANGLE; THENCE ALONG SAID MALE ROTOR LOBE RADIUS ARC IN A DIRECTION GENERALLY COUNTER TO THE DIRECTION OF ROTATION TO THE INTERSECTION OF SAID ARC WITH THE RADIAL LINE EXTENDING TO THE CENTER OF SAID CONCENTRICALLY MOUNTED ROTOR FROM THE POINT FROM WHICH SAID ARC WAS STRUCK; THENCE THROUGH A POINT AT WHICH THE FEMALE LOBE AND MALE LOBE SPACE ARE IN SUBSTANTIALLY COMPLETE ENGAGEMENT TO A POINT ON SAID FIRST CIRCLE ARC REMOVED SUBSTANTIALLY 180* IN THE DIRECTION OF ROTATION FROM THE CENTER LINE OF SAID FILLED ROTOR LOBES; AND THENCE ALONG SAID FIRST CIRCLE ARC TO THE PLACE OF BEGINNING. 